Fig. 2.
Annual ambient PM2.5 air quality standards worldwide
PM2.5: mass concentration of aerosol particles smaller than approximately 2.5 μm.
Note: Data for China are the commercial PM2.5 standard.
Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.